JPH0393450A - Rotational position detector in motor - Google Patents

Abstract

PURPOSE:To enable a magnetic sensor to be arranged close to the magnet of a rotor section by forming partially magnetized sections for showing reversed polarities against the polarities of magnetic poles, on the all magnetic poles of the same polarizes of the magnet except one specific magnetic pole. CONSTITUTION:A magnetic sensor 19 is fitted on a printed board 10. The magnet 18 of a rotor is n/s-magnetized in the radial direction, and is magnetized to be alternately divided along the peripheral direction. Then, on the all magnetic poles (n poles) of the same polarities of the magnet 18 except one specific magnetic pole, partially magnetized sections for showing reversed polarities (s poles) against the magnetic poles of the same polarities are formed on the inner peripheral side. As a result, by the output signal of the magnetic sensor 19, magnetic flux is almost cancelled at the reversed magnetized sections, and output from the sections of non-reversed magnetization only is increased, and the rotational position of a motor can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a rotational position detecting device for a motor used for detecting switching timing of a VTR cylinder head or detecting an index of a floppy disk. [Prior Art] Generally, as a rotational position detection device for a motor of this kind, a PG magnet (III) for position detection is provided on the outer periphery of the rotor portion of the motor, and a PG magnet (III) for detecting the position is provided in the stator portion. P for detecting rotational position
A model equipped with a G head is known. In such a rotational position detection device for a motor, PG
In addition to requiring a magnet, it also had the disadvantage of requiring an expensive component called a PG head. Conventionally, the Tokuma 62-1759 device was developed as a rotational position detection device for a motor that did not require the above-mentioned PG magnet or expensive parts such as a PG head.
The one shown in Publication No. 52 is known. The rotational position detection device for a motor disclosed in the above publication is applied to a VTR, and as shown in FIG. A stator section is constituted by a drive coil 2 and a printed circuit board 3, and a magnet yoke 7 fixed via a collar blade 6 to a shaft 5 supported by a bearing 4 fixed to the stator section; A rotor section is constituted by a magnet 8 fixed to the rotor. This magnet 8 has a donut-like shape, and its plane is divided into 12 parts, which are alternately divided into n. It is magnetized to s. Of the magnetic poles of the same polarity of the magnet 8 that have been magnetized in a divided manner, all of the magnetic poles except one specific magnetic pole are formed with partially magnetized portions having a polarity opposite to that of the magnetic pole.

On the other hand, in the figure, the printed circuit board 3 has a printed pattern (not shown) for frequency power generation of an all-around integral type on the lower surface (the side closer to the magnet 8), and a magnetic sensor made of a Hall element on the upper surface in the figure. (not shown) is provided. That is, the structure of this motor is of a surface facing type as shown in the figure, and the magnetic sensor that detects the magnetic field of the magnet 8 is attached to the surface opposite to the magnet 8 with the printed circuit board 3 in between. ing.

In the rotational position detection device for the motor as described above,
The rotor portion rotates due to the electromagnetic action of the magnetic field generated by the drive current flowing through the drive coil 2 and the magnet 8. Due to this rotation, an electromotive force having a frequency corresponding to the rotation is generated in the printed pattern for frequency power generation, thereby controlling the rotation speed of the rotor section. Further, in the magnetic sensor, a stronger magnetic flux is detected from a portion of the magnet 8 where a partially magnetized portion having the opposite polarity is not formed than a portion where the partially magnetized portion is formed. The magnetic sensor detects the portion where the partially magnetized portion is not formed, and thereby the switching timing of the cylinder head rotated by the shaft 5 can be detected. The rotational position detection device for a motor as described above does not require the above-mentioned PG magnet, nor does it require an expensive PG head. [rRa to be solved by the invention] By the way, in the rotational position detection device for the motor described with reference to FIG. The distance from the upper end surface to the magnetic sensor cannot be made smaller than the thickness of the printed circuit board 3, which has the drawback of degrading the S/N of the detection signal. In order to make this S/N good, in order to bring the magnetic sensor close to the magnet 8, (1) provide a hole for inserting the magnetic sensor in the printed circuit board 3, or (2) place the magnetic sensor on the lower side of the printed circuit board 3 in the figure. It is also possible to consider other means such as arranging it.

However, the method (2) has the disadvantage that the process of drilling holes in the printed circuit board 3 is increased, and a printed pattern cannot be formed in the holes, making the wiring complicated.
The disadvantage of this method is that the distance from the magnet 8b) to the drive coil 2 increases by the amount of the magnetic sensor, and the driving force of the motor decreases. The present invention eliminates the above-mentioned drawbacks and provides a rotational position detection device for a motor in which a magnetic sensor can be easily disposed close to the magnet of the rotor. [Means for Solving the Problems] In order to solve the above problems, the present invention provides a cylindrical structure that is magnetized in the radial direction in n and s, and that is alternately divided along the circumferential direction. A motor configured with a rotor part made up of a magnet, and a stator part made up of a plurality of drive coils having a core in a radial direction and facing circumferentially to the magnetized surface of the magnet. a magnetic sensor for detecting the magnetic flux of the magnet, and a partially magnetized portion having a polarity opposite to that of the magnetic pole is formed on all magnetic poles of the magnet of the same polarity except for one specific magnetic pole. , the rotational position of the motor is detected by the output of the above-mentioned magnetic sensor, and also, among both the n and s magnetic poles of the magnet, all magnetic poles except a specific one magnetic pole have respective magnetic poles. A partially magnetized portion having a polarity opposite to the polarity may be formed, and the magnetic sensor outputs a mixture of a switching signal for a motor drive coil and a signal indicating a rotational position of the motor. It is also possible to do so.

[Function] In the rotational position detecting device for a motor configured as described above, the magnetic sensor has a partially magnetized part showing the opposite polarity from a magnetic pole that does not have a partially magnetized part showing the opposite polarity. A magnetic flux stronger than that of the other magnetic poles formed is detected, and this allows the rotational position of the rotor to be detected. In addition to the above-mentioned signal indicating the rotational position, the magnetic sensor also provides a switching signal for the drive coil of the motor, which allows the current of the drive coil to be switched to control the rotational speed of the motor. [Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. Figure 1 is a vertical front view of the motor, Figure 2 is a perspective view partially showing the magnet, Figure 3 is a developed view showing the state of magnetization of the magnet, and Figure 4 is the output signal detected by the magnetic sensor. This is a waveform diagram. In Figure 1, reference numeral 1
0 is a printed circuit board, and the printed circuit board is fixed member 1
It is fixed at l. A stator core l2 is fixed to this fixing member l1, and a drive coil 13 is fixed to the stator core.
is wound. The stator section is composed of the printed circuit board 10, the fixing member 11, the stator core 12, and the drive coil 13. A shaft 15 is rotatably supported on the fixed member 11 via a bearing 14 .

Reference numeral 16 denotes a magnetic yoke, which is fixed to the aforementioned shaft l5 via a collar blade l7. A cylindrical magnet l8 is fixed to this magnetic yoke l6. These magnet yoke 16, collar preload l7, and magnet l8 constitute a rotor section. Reference numeral 19 denotes a magnetic sensor made of a Hall element or the like, which is attached to the printed circuit board 10 described above. As shown in FIGS. 2 and 3, the above magnet 1B has n. s, and this is divided and magnetized alternately along the circumferential direction (the figure shows an 8-pole magnet), and a specific one of the magnets of the same polarity [+ (n poles)] All the magnetic poles except the magnetic pole are formed with a partially magnetized portion on the inner circumferential side having a polarity opposite to that of the magnetic pole (S pole).

The drive coil 13 is composed of a plurality of coils that circumferentially face the neutral magnetic surface of the magnet 18 and have a core in the radial direction.

In the rotational position detecting device for a motor configured as described above, the rotor section receives a drive torque and rotates, as is well known, due to the electromagnetic action of the drive current flowing through the drive coil l3 and the magnet 18. Further, the magnetic sensor l
The output signal of No. 9 is as shown in Figure 4, and the magnetic flux is almost canceled out in the reversely magnetized portion, and the output only from the non-reversely magnetized portion becomes large, which makes it possible to detect the rotational position of the motor. becomes possible. In the above embodiment, a partially magnetized portion having a polarity opposite to that of the magnetic pole was formed on all of the magnetic poles of the magnet l8 having the same polarity except for one specific magnetic pole. As shown, among both the n and s magnetic poles of magnet l8,
Partially magnetized portions having a polarity opposite to that of each magnetic pole may be formed on all magnetic poles except one specific magnetic pole. In this case, the output of the magnetic sensor 19 will be as shown in FIG. 6, S/N
becomes even better. Furthermore, as shown in FIG. 7, by reducing the area of the partially magnetized portion, the magnetic sensor l9 can output both the switching signal of the motor drive coil 13 and the signal indicating the rotational position of the motor. Since the signals are mixed and output, the number of parts can be reduced compared to the case where the means for obtaining the switching signal of the drive coil l3 and the means for obtaining the signal indicating the rotational position are provided separately. FIG. 8 shows an output waveform diagram of the magnetic sensor l9 when both the switching signal of the drive coil l3 and the signal indicating the rotational position are mixed and output. [Effects of the Invention] As described above, the present invention provides a rotational position detection device for a motor that can output a detection signal with a good S/N ratio because the magnetic sensor l9 can be disposed close to the magnet l8. is obtained.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view of a motor showing an embodiment of the present invention, Fig. 2 is a perspective view showing a part of the main parts of Fig. 1, and Fig. 3 is a developed view showing the main parts of Fig. 1. , FIG. 4 is a waveform diagram showing the detection output of the one in FIG. 1, FIG. 5 is an expansion diagram showing another embodiment, and FIG. 6 is a waveform diagram showing the detection output of the one in FIG. 5.
FIG. 7 is a developed view showing still another embodiment, FIG. 8 is a waveform diagram showing the detection output according to the one shown in FIG. 7, and FIG. 9 is a longitudinal sectional front view of the motor showing a conventional example. 10: Printed circuit board, 13: Stator core, 15: Shaft,
l6: Magnet yoke, l8: Magnet, 19: Magnetic sensor.

Claims (3)

[Claims] (1) a rotor portion consisting of a cylindrical magnet magnetized in n and s directions in the radial direction and magnetized in sections alternately along the circumferential direction; A motor configured with a stator section consisting of a plurality of drive coils each having a core in the radial direction, the motor comprising a magnetic sensor disposed on a substrate to detect the magnetic flux of the magnet, and a stator section consisting of a plurality of drive coils each having a core in the radial direction. A partially magnetized portion having a polarity opposite to that of the magnetic pole is formed on all of the magnetic poles except one specific magnetic pole, and the rotational position of the motor is detected by the output of the magnetic sensor described above. A rotational position detection device for a motor, characterized by: (2) A partially magnetized portion having a polarity opposite to that of the respective magnetic poles is formed on all of the magnetic poles of both the N and S magnetic poles of the magnet, except for one specific magnetic pole. A rotational position detection device for a motor according to claim 1. (3) The motor according to claim 1, wherein the magnetic sensor outputs both a switching signal for a drive coil of the motor and a signal indicating a rotational position of the motor in a mixed manner. Rotary position detection device.